Metal d x 2 -y 2 NH 3 Right symmetry for interaction Metal d xy Wrong symmetry for interaction x y NH 3 x So, (3d z 2 , & 3d x 2 -y 2 ) & 2 lone pair orbitals interact to form sigma bonds d xy , d xz , d yz do NOT y Octahedral Case: Ligands along x, y, z axes σ-bonding: Molecular Orbital Theory (LCAO-MO) applied to Coordination Compounds: Metal Atom Orbitals (ligands along x, y, z axes) (3d z 2 , & 3d x 2 -y 2 ) Ligands (6 lone pair orbitals) Ligand Field Theory
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Metal dx2-y2
NH3
Right symmetry for interaction
Metal dxy
Wrong symmetry for interaction
x
y
NH3x
So, (3dz2, & 3dx2-y2) & 2 lone pair orbitals
interact to form sigma bonds
dxy, dxz, dyz do NOT
y
Octahedral Case: Ligands along x, y, z axes
σ-bonding: Molecular Orbital Theory (LCAO-MO)
applied to Coordination Compounds: Ligand Field Theory
Metal Atom Orbitals (ligands along x, y, z axes)
(3dz2, & 3dx2-y2)
Ligands (6 lone pair orbitals)
Ligand Field Theory
SALC
(sigma)6 0 0 2 2 0 0 0 4 2 = A1g + Eg + T1u
Reducible Representation Decompose into three
Irreducible Representations
Ligand Field Theory: Oh Complexes
FIGURE 20.16
SALCs Resource section 5
Symmetry of d orbitals From Oh character table
Crystal Field Splitting of
Tetrahedral Complexes
e = low energy
t2 = high energy (closer to corners)
note: NO “g” subscripts for d orbital symmetry in tetrahedral geometry(the Td point group does not have the inversion symmetry)
Ligand Field Theory: Td Complexes
SALCs from Resource section 5
Metal ML4 4 Ligands
3d
4s
4pT2
A1
E+T2
s
A1+T2
a1
a1
t2
t2
t2
Metal ML4 4 Ligands
3d
4s
4pT2
A1
E+T2
s
A1+T2
a1
a1
t2
t2
t2
e
DT
Crystal Field Splitting
Tetrahedral Complexes
No low-spin tetrahedral complexes!
Dt= -4/9 Do
Extent of splitting from p - bonding: Weak and Strong Field ligands
Consider Cl- (weak), NH3 (intermediate) and CO (strong)
CASE 1: NO p-INTERACTION = σ-DONOR (i.e. NH3)
Metal dx2-y2
NH3x
y
Extent of splitting from p - bonding: Weak and Strong Field ligands
Consider Cl- (weak), NH3 (intermediate) and CO (strong)
Cl M
- bonding as before
Now p - bonding between p & dxy, dxz, dyz
σ - bonding as before
Now p - bonding between CO p * & dxy, dxz, dyz
No p - bonding with CO p
M
CASE 2: p-DONOR (i.e. Cl-)
CASE 3: p -ACCEPTOR (i.e. CO)
CASE 1: NO p-INTERACTION = σ-DONOR (i.e. NH3)
N C
SALCs from Resource section 5
dxy, dxz, dyz
d* = eg
= t2g
σ metal-ligand molecular orbitals
(all filled, mostly ligand character)
6 ligand donor orbitals
(sigma symmetry)
Metal LigandMolecule
Metal-Ligand Bonding: Sigma-DONOR Ligands, NO pi-bonding
The backbonding effect stabilizes the complex because the overall charge transfer can be adjusted to fit both the ligand and metal “needs”: if the metal would like to have more or less electrons, it can adjust the amount of backdonation to the ligand.
Backdonation tends to favor low-oxidation state metals, such as Ti(0) or Cr(0) for instance.